1. Field of the Invention
The present invention relates to small internal combustion engines of the type used for lawn mowers, lawn and garden tractors, snow throwers and other implements, or with small sport vehicles. Particularly, the present invention relates to a priming system to aid in starting such engines.
2. Description of the Related Art
Small internal combustion engines typically include a carburetor which mixes liquid fuel with atmospheric air drawn through the carburetor to provide an air/fuel combustion mixture to the engine. One type of carburetor commonly used in small engines includes a throat with a venturi through which air is drawn, and into which fuel is drawn for mixing with the intake air. A fuel bowl is disposed beneath the throat in which a quantity of liquid fuel is stored. A float valve in the fuel bowl meters the supply of fuel thereinto from the main fuel tank as necessary as the fuel in the fuel bowl is consumed.
Additionally, such carburetors typically include a manually operable priming feature, such as a flexible priming bulb which is depressed by an operator to pressurize the air space above the fuel in the fuel bowl, thereby forcing a quantity of priming fuel into the carburetor throat for mixing with the intake air which is drawn into the carburetor. The priming fuel is in excess of the amount of fuel which is normally supplied for mixing with the intake air to form a combustion mixture, such that rich air/fuel mixture is initially supplied to the engine to aid in engine starting. After the engine starts, the priming fuel is consumed, and mixing of the air/fuel mixture is thereafter controlled by the fuel metering system of the carburetor during running of the engine.
The foregoing priming feature for carburetors requires an operator to manually press the flexible priming bulb at the location of the carburetor in order to prime the engine. Although remote priming devices which utilize a cable operably connected between the handle of an implement and the flexible priming bulb of the carburetor have been devised, such devices typically require multiple actuations thereof by an operator in order to build sufficient air pressure within the carburetor bowl to properly pressurize same.
Additionally, actuation of such priming mechanisms when the engine is already in a warm condition, such as during warm engine re-starts, may provide an unnecessarily rich fuel/air mixture to the engine which could flood the engine.
It is desirable to provide a priming system for use in small internal combustion engines having carburetors which is an improvement over the foregoing.
The present invention provides a priming system for a carburetor for small internal combustion engines, wherein the priming system is remotely actuated and includes an automatic primer disabling feature operative when the engine is in a warm condition to prevent the supply of an overly rich fuel/air mixture to the engine intake system during warm re-starts, for example.
A bail assembly on the implement with which the engine is used is connected via cable linkage to a rotatable cam member of the carburetor. When the bail is actuated prior to starting the engine, translation of the cable rotates the cam member to engage a cam surface thereof with a plunger of the carburetor to depress the plunger. Depression of the plunger forces a quantity of fuel from a priming chamber, defined between the plunger and the carburetor body, into the throat of the carburetor to provide a rich fuel/air mixture for engine priming.
After an initial quantity of fuel is forced from the priming chamber into the throat of the carburetor, a further quantity of fuel remains within the priming chamber and is gradually drawn into the throat of the carburetor during an initial running period of the engine to provide an enriched air/fuel mixture to the engine until the priming chamber is empty of liquid fuel. In this manner, the present priming system provides an initial amount of fuel for engine starting, and also provides an extended priming feature.
Additionally, the present priming system includes a thermally-responsive element operable during warm engine temperatures to disable the priming function. Specifically, a disk is rotatably mounted to the carburetor body within the priming chamber, and a thermally responsive element, such a bimetallic spring, is connected between the disk and the carburetor body. When the engine is cold, the bimetallic spring positions the disk in a first position wherein an opening in the disk is aligned with the priming passage connecting the priming chamber to the throat of the carburetor, such that liquid fuel may be forced therethrough for priming. Additionally, in the first disk position, a flap valve portion of the disk is aligned with a fuel supply passage which connects the fuel bowl to the priming chamber, and acts as a check valve such that when the plunger is depressed, fuel may only be forced through the priming passage to the throat of the carburetor.
When the engine reaches a warm operating temperature, the bimetallic spring rotates the disk to a second position in which the aperture thereof is not aligned with the priming passage and supply of priming fuel from the priming chamber through the priming passage to the throat of the carburetor is blocked to thereby disable the priming function. Also, in the second disk position, the flap valve portion of the disk is not aligned with the fuel supply passage, such that fuel may pass between the fuel bowl and the priming chamber.
The bimetallic spring is adjustably connected to the disk in order to vary the point of connection therebetween. In this manner, the disablement of the priming function can be properly correlated to an engine temperature at which is desired to disable the priming function.
Advantageously, the present invention provides a remotely-actuated priming system, eliminating the need for an operator to prime the carburetor at the location of the carburetor. Further, the thermally-responsive element is actuated at warm engine temperatures to disable the priming function, such that the engine cannot be primed during warm re-starts and flooding of the engine is less likely.
In one form thereof, the present invention provides an internal combustion engine, including an engine housing; a carburetor attached to the engine housing, the carburetor having a throat; a plunger moveably connected to the carburetor, the plunger and the carburetor defining a variable-volume priming chamber therebetween in which a quantity of liquid fuel is disposed; a plunger actuator moveably coupled to the plunger; and a thermally-responsive element disposed within the priming chamber, the element moveable between a first position in which the priming chamber is in fluid communication with the throat and a second position in which fluid communication between the priming chamber and the throat is blocked; whereby when the element is in the first position, movement of the plunger actuator moves the plunger to force at least a portion of the liquid fuel from the priming chamber into the throat.
In another form thereof, the present invention provides an internal combustion engine, including an engine housing; a carburetor attached to the engine housing, the carburetor having a throat; a plunger connected to the carburetor, the carburetor and plunger defining a priming chamber therebetween in which a quantity of liquid fuel is disposed; remotely actuable means for depressing the plunger to force at least a portion of the liquid fuel from the priming chamber into the throat; and thermally-responsive means disposed within the priming chamber for preventing injection of liquid fuel from the priming chamber into the throat when the engine is in a warm condition.
In a further form thereof, the present invention provides an implement, including a frame having a handle; a bail assembly attached to the handle; an engine connected to the frame and including a carburetor, the carburetor including a housing having a throat therethrough; a plunger connected to the housing and defining a priming chamber therebetween in which a quantity of liquid fuel is disposed, the plunger depressible by actuation of the bail assembly to force at least a portion of the liquid fuel from the priming chamber into the throat; and a thermally-responsive element moveable between a first position in which the priming chamber is in fluid communication with the throat and a second position in which fluid communication between the priming chamber and the throat is blocked.
In a further form thereof, the present invention provides a method of operating an implement having an internal combustion engine with a carburetor, including the steps of actuating a bail assembly of the implement which is connected to a plunger of the carburetor; depressing the plunger by actuation of the bail assembly to reduce the volume of a priming chamber defined between the plunger and a housing portion of the carburetor in which a quantity of liquid fuel is disposed; forcing at least a portion of the liquid fuel from the priming chamber into a throat of the carburetor to prime the carburetor; starting the engine; and disabling the priming of the carburetor by preventing passage of fuel from the priming chamber into the throat of the carburetor when the engine reaches a warm operating temperature.